1. Field of the Invention
The present invention relates to techniques for navigation systems to calculate a current position.
2. Description of the Related Art
In a navigation system, techniques for calculating a current position such as two dimensional map-matching are known. In two dimensional map-matching, a navigation system calcules a current position on a road by map-matching between a road on a two-dimensional map and a two dimensional position in longitudinal and latitudinal directions or a track of the two dimensional position, which is measured by satellite positioning or autonomous navigation.
Techniques are known in such two dimensional map-matching to solve a problem of miscalculating a current position after passing of a branch point at which a road branches at a narrow angle. That is, in a known technique, after passing of a branch point at which a road branches at a narrow angle, a current position is calculated by performing, with each road branching at the branch point as a candidate road, map-matching in an altitude direction in which a matching degree between a gradient of each candidate road indicated by map data and an inclination detected by an inclination angle sensor is a reference (see, for example, JP 2003-194558 A and JP 10-253373 A).